Methods of cementing in subterranean zones and cementing compositions therefor

ABSTRACT

A method and cementing composition is provided for sealing a subterranean zone penetrated by a well bore, wherein the cementing composition comprises a mixture of cementitious material, a polymeric cement cohesion additive, and sufficient water to form a slurry. The polymeric cement cohesion additive is a high molecular weight hydroxyethylcellulose. The method comprises placing the cement composition in the subterranean zone and allowing the cement composition to set into a solid mass therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of pending U.S.patent application Ser. No. 10/900,651 filed Jul. 28, 2004, the entirecontents of which is incorporated by reference herein.

BACKGROUND

The present embodiment relates generally to a method of cementing andcementing compositions for sealing a subterranean zone penetrated by awell bore.

In the drilling and completion of an oil or gas well, a cementingcomposition is often introduced in the well bore for cementing pipestring or casing. In this process, known as “primary cementing,” thecementing composition is pumped into the annular space between the wallsof the well bore and the casing. The cementing composition sets in theannular space, supporting and positioning the casing, and forming asubstantially impermeable barrier, or cement sheath, which isolates thewell bore into subterranean zones. The objective of primary cementing isto prevent the undesirable migration of fluids between such subterraneanzones.

Conventional cement compositions, however, mix readily with fluids inthe well bore. It has been found that the admixture of as little as twopercent of well bore fluid with a cement slurry will contaminate thecement slurry and degrade the competency of the slurry.

Balanced plugs and wells cemented in the presence of oil-based drillingmuds (invert muds) are susceptible to well bore fluid contaminationduring placement. When a cement plug is contaminated with as little astwo percent wellbore fluid during placement, it can cause: a slowsetting cement plug which results in longer cementing times andincreased rig costs, a contaminated cement plug top which results in theneed to drill further into the plug to obtain a competent cement top,gas migration, an incompetent cement plug from top to bottom requiring asecond plug attempt, and a washed away or diluted cement plug requiringa second plug attempt.

Success is also low with shallow cement plugs which tend to leak andthis can be attributed to the cement plugs mixing with mud systemsand/or well bore fluids. Invert plug successes also tend to be low andsuch poor results in most instances can be attributed to the mixing ofthe cement slurry with the mud system.

Success on invert foam cement jobs is also low due to gas breakoutresulting in a poor foam cement job. Gas breakout on such invert foamcement jobs can also be attributed to contamination of the invert foamcement with well bore fluids.

In foam cementing, the admixture of as little as two percent of anoil-based or invert mud will de-stabilize the foam. The de-stabilizationof the foam and resultant gas breakout results in higher than desireddensity thus increasing hydrostatic pressure, gas migration and cementfall back caused by a lower than anticipated cement top.

Therefore, a cementing composition incorporating cement, but havingsufficient cohesion to avoid contamination, is desirable for cementingoperations.

DESCRIPTION

A non-foamed cementing composition for sealing a subterranean zonepenetrated by a well bore according to the present embodiment comprisesa mixture of cementitious material (“cement”), a polymeric cementcohesion additive, and sufficient water to form a slurry.

A foamed cement composition useful in accordance with the presentembodiment is comprised of a cement, a polymeric cement cohesionadditive, sufficient water to form a slurry, a mixture of foaming andfoam stabilizing surfactants present in an amount sufficient to foam andstabilize a foamed cement composition, and sufficient gas to form afoam.

The cementing composition according to the present embodiment can beused in a variety of cementing operations including foam cementing, plugcementing (open and cased hole), primary and squeeze cementing,cementing during drilling operations when encountering washed out zoneswith high leakoff and as a cement spacer additive. Preferably, thecement composition of the present embodiment is used in open hole andcased hole plug cementing as well as foam cementing in the presence ofboth oil-based and water-based well bore fluids.

The polymeric cement cohesion additive of the cement composition of thepresent embodiment maintains the cohesiveness of the cement slurry whilemaintaining acceptable rheological properties. The polymeric cementcohesion additive prevents contamination or mixture of the cement slurrywith the well bore fluids and reduces the effects of wash out ordilution with water based and/or oil based well bore fluids. It isanticipated that when the cement composition at the leading edge of acement plug includes the polymeric cement cohesion additive, reducedcontamination and increased job success will be achieved.

The methods according to the present embodiment of cementing insubterranean zones penetrated by well bores utilizing foamed ornon-foamed cement compositions containing a polymeric cement cohesionadditive meet the needs described above and overcome the deficiencies ofthe prior art. That is, because, as noted above, the polymeric cementcohesion additive inhibits cement contamination and/or dilution withboth oil-based and water-based wellbore fluids and thus increases thecompetency and success of the cement plug while maintaining acceptableTheological properties. Additionally, the polymeric cement cohesionadditive reduces fluid loss, slightly increases the viscosity of thecement slurry and causes little or no retardation. The polymeric cementcohesion additive produces a superior cement plug, reduces failures andincreases the number of successful cementing jobs on the first attemptthus reducing costly secondary jobs. In foam cementing jobs, thepolymeric cement cohesion additive minimizes and/or eliminates thepotential for gas breakout. The polymeric cement cohesion additive hasapplications for use on both land-based and off-shore cementingprograms.

The polymeric cement cohesion additive can be dry blended into thecement or the polymeric cement cohesion additive can be prehydrated intothe cement mix fluid, i.e. mix water, to be used for a cement plug or aliquid form of the polymeric cement cohesion additive can be added onthe fly to a cement slurry.

The methods according to the present embodiment utilizing a non-foamedcement composition include the following steps. A cement composition isprepared comprised of cement, a polymeric cement cohesion additive, andsufficient water to form a slurry. The cement composition is then placedinto a subterranean zone and allowed to set into a solid mass therein.

The methods according to the present embodiment utilizing a foamedcement composition are the same as described above for non-foamed cementcompositions except that the prepared cement composition is comprised ofa cement, a polymeric cement cohesion additive, sufficient water to forma slurry, a mixture of foaming and foam stabilizing surfactants presentin an amount sufficient to foam and stabilize a foamed cementcomposition and sufficient gas to form a foam.

A variety of cements can be used with the present embodiment, includingcements comprised of calcium, aluminum, silicon, oxygen, and/or sulfur,which set and harden by reaction with water (“hydraulic cements”). Suchhydraulic cements include Portland cements, pozzolan cements, gypsumcements, aluminous cements, silica cements, and alkaline cements.Portland cements or their equivalents are generally preferred for use inaccordance with the present invention when performing cementingoperations in subterranean zones penetrated by well bores. Portlandcements of the types defined and described in API Specification ForMaterials and Testing For Well Cements, API Specification 10, 5^(th)Edition, Jul. 1, 1990, of the American Petroleum Institute (the entiredisclosure of which is hereby incorporated as if reproduced in itsentirety) are preferred. Preferred API Portland cements include ClassesA, B, C, G, and H, of which API Classes A, G and H are particularlypreferred for the present embodiment. It is understood that the desiredamount of cement is dependent on the volume required for the sealingoperation.

The polymeric cement cohesion additive of the present embodiment is ahigh molecular weight hydroxyethylcellulose. The hydroxyethylcellulosehas a molecular weight of at least 300,000 g/mol, or 1,300,000 g/mol. Aswill be understood, the amount of the polymeric cement cohesion additiveincluded in the cement compositions of the present embodiment can varydepending upon the temperature of the zone to be cemented and theparticular pumping time required. Generally, the polymeric cementcohesion material is included in foamed and non-foamed cementcompositions in an amount of at least about 0.2% by weight of cement(bwoc) or 0.45% bwoc in the composition.

The water used to form the slurry is present in an amount sufficient tomake the slurry pumpable for introduction down hole. The water used toform a slurry in the present embodiment can be fresh water or saltwater. The term “salt water” is used herein to mean salt solutionsranging from unsaturated salt solutions to saturated salt solutions,including brines and seawater. Generally, any type of water can be used,provided that it does not contain an excess of compounds well known tothose skilled in the art, that adversely affect properties of thecementing composition. Generally, the water is present in the cementcompositions in an amount in the range of from about 25% to about 170%by weight of the cement therein, so as to yield cement compositionshaving a density of from about 11.6 lb/gal to about 19.2 lb/gal.

A variety of additives may be added to the cementing composition toalter its physical properties. Such additives may include slurry densitymodifying materials (e.g., silica flour, silica fume, sodium silicate,microfine sand, iron oxides and manganese oxides), dispersing agents,set retarding agents, set accelerating agents, fluid loss controlagents, strength retrogression control agents, viscosifying agents,foaming agents and foam stabilizing agents well known to those skilledin the art.

When a foamed cement composition is utilized, a mixture of foaming andfoamed stabilizing surfactants present in an amount sufficient to formand stabilize a foamed cement composition is included in the cementcomposition. A preferred mixture of foaming and foam stabilizingsurfactants for use in accordance with the present embodiment iscomprised of an ethoxylated alcohol ether sulfate of the formulaH(CH₂)_(a)(OC₂H₄)_(b)OSO₃NH₄ ⁺ wherein a is an integer in the range offrom about 6 to about 10 and b is an integer in the range of from about3 to about 10, an alkyl or alkene amidopropylbetaine having the formulaR-CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂CO₂ ⁻ wherein R is a radical selected from thegroup of decyl, cocoyl, lauryl, cetyl and oleyl and an alkyl or alkeneamidopropyldmethylamine oxide having the formulaR—CONHCH₂CH₂CH₂N⁺(CH₃)₂O⁻ wherein R is a radical selected from the groupof decyl, cocoyl, lauryl, cetyl and oleyl.

The ethoxylated alcohol ether sulfate is generally present in the abovedescribed mixture in an amount in the range of from about 60 to 64 partsby weight. The alkyl or alkene amidopropylbetaine is generally presentin the mixture in an amount in the range of from about 30 to about 33parts by weight and the alkyl or alkene amidopropyldimethylamine oxideis generally present in the additive in an amount in the range of fromabout 3 to about 10 parts by weight. In order to make the surfactantmixture more easily combinable with the cement slurry, water can becombined with the mixture in an amount sufficient to dissolve thesurfactants.

The most preferred foaming and foam stabilizing surfactant mixture ofthe type described above for use in accordance with this embodiment iscomprised of an ethoxylated alcohol ether sulfate wherein a in theformula set forth above is an integer in the range of from 6 to 10 andthe ethoxylated alcohol ether sulfate is present in the surfactantmixture in an amount of about 63.3 parts by weight; the alkyl or alkeneamidopropylbetaine is cocoylamidopropylbetaine and is present in themixture in an amount of about 31.7 parts by weight and the alkyl oralkene amidopropyldimethylamine oxide is cocoylamidopropyldimethylamineoxide and is present in an amount of about 5 parts by weight.

The mixture of foaming and foam stabilizing surfactants is generallyincluded in the foamed cement composition as a 30% to 50% aqueoussolution in an amount in the range of from about 0.5% to about 5% byvolume of water in the cement slurry, preferably in an amount of fromabout 1% to about 3%.

The gas utilized for foaming the cement slurry can be air or nitrogen,with nitrogen being preferred. The gas is present in an amountsufficient to foam the slurry, generally in an amount in the range offrom about 10% to about 35% by volume of the slurry.

A particularly preferred foamed cement composition for use in accordancewith this embodiment is comprised of Portland cement; a polymeric cementcohesion additive present in an amount of at least 0.3% by weight ofcement in the composition; sufficient water to form a slurry; a mixtureof foaming and foam stabilizing surfactants comprised of an ethoxylatedalcohol ether sulfate present in the mixture in an amount of about 63.3parts by weight; cocoylamidopropylbetaine present in the mixture in anamount of about 31.7 parts by weight and cocoylamidopropyldimethylamineoxide present in the mixture in an amount of about 5 parts by weight;the mixture being present in the cement composition as a 30% to 50%aqueous solution in an amount in the range of from about 1% to about 3%by volume of water in the cement composition; and sufficient gas to forma foam.

The water used is preferably included in the above described foamedcement composition in an amount in the range of from about 35% to about55% by weight of hydraulic cement therein and the gas, preferablynitrogen, is preferably present in the composition in an amount in therange of from about 15% to about 30% by volume of the composition.

In order to further illustrate the methods and cement compositions ofthis embodiment, the following examples are given.

EXAMPLE 1

A conventional cement slurry was injected into a graduated cylindercontaining water. The slurry immediately disseminated throughout thewater, thus diluting and contaminating the sample. Upon standing, thesample settled, however, the sample was contaminated and diluted withwater. Once the conventional cement slurry settled, the volume hadalmost doubled. The increased volume was due to waterdilution/contamination. Upon the slurry setting, decreased compressivestrength resulted from the dilution/contamination effect of the water.

EXAMPLE 2

Cement compositions including hydroxyethylcellulose (HEC) additives ofdifferent molecular weight were tested to determine the effectiveness oftheir cohesive properties while maintaining acceptable Theologicalproperties. A cement slurry was determined to have acceptable cohesiveproperties under laboratory test conditions as follows. A cement slurrycontaining HEC was aspirated into a syringe. The cement slurry was theninjected into a water-filled graduated cylinder. The slurry maintainedthe diameter of the aperture from which it was extruded and formed along malleable string while falling to the bottom of the graduatedcylinder. It did not readily disperse or commingle with the water. Oncethe slurry began to mound on the bottom of the graduated cylinder itformed one cohesive mass. Those cement slurries that fell from thesyringe to the bottom of the water-filled graduated cylinder withoutdispersing into the water or gain substantial volume due todilution/contamination, were determined to have acceptable cohesiveproperties.

The specific procedure was as follows:

-   -   1) 200 mL of tap water was placed in a 250 mL graduated        cylinder.    -   2) A cement blend (0:1:0 Class G Cement (1895 kg/m³, Water        Requirement 0.44 m³/t and Yield 0.77 m³/t)+X % HEC) was mixed        for 2 minutes at 200 rpm in a Waring blender jar.    -   3) Using a 60 mL syringe, 50 mL of slurry was obtained.    -   4) The tip of the syringe was submerged just below the surface        of the water and the slurry was slowly extruded into the        graduated cylinder.    -   5) The heights of both cement and intermediate phase right after        the slurry was placed in the graduated cylinder and these values        were recorded for T=0 min.    -   6) The heights of both cement and intermediate phase were then        recorded at T=5 min, 10 min, 20 min, 30 min and 60 min.    -   7) During the first 5 minutes of each test, rheology readings        were recorded from the remaining slurry at 600 rpm, 300 rpm, 200        rpm, 100 rpm, 6 rpm and 3 rpm. The rheology readings were taken        using a Fann 35 viscometer with a F1 spring, B1 bobb and R1        rotor.

Four different HEC additives of different molecular weight were testedto determine their relative effectiveness as a cement cohesion additivewhile maintaining acceptable rheological properties. In addition, theHEC additives were tested at a rate of 0.5% bwoc and 0.25% bwoc. Thespecific HEC additives each of which is commercially available fromHercules Incorporated—Aqualon Division, Houston, Tex. were as follows:

HEC 250 HHR having a molecular weight of 1,300,000 g/mol;

HEC 250 GXRCP having a molecular weight of 300,000 g/mol;

HEC 250 LR PA having a molecular weight of 90,000 g/mol; and

HEC 250 JR which is a blend of two HEC additives and does not have aspecific molecular weight.

The results of these tests are set forth below in Tables I-IV: TABLE IHEC Additives at 0.5% (bwoc) CEMENT HEIGHT (mL)/INTERMEDIATE HEIGHT (mL)Exhibits # Additive 0 min 5 min 10 min 20 min 30 min 60 min Cohesion 1HEC 250 HHR 53/0 52/0 52/0 52/0 52/0 52/0 YES 2 HEC 250 GXRCP 53/21261/220 60/218 60/218 50/60 50/68 YES 3 HEC 250 JR 13/234 20/230 58/23046/230 44/230 46/232 NO 4 HEC 250 LR 68/232 66/230 62/230 48/229 46/22946/228 NO

TABLE II HEC Additives at 0.5% (bwoc) Rheology 600 # Additive rpm 300rpm 200 rpm 100 rpm 6 rpm 3 rpm 1 HEC 250 HHR >300 >300 >300 >300 204151 2 HEC 250 GXRCP >300 >300 243 150 43 38 3 HEC 250 JR 226 128 92 5411 8 4 HEC 250 LR 175 94 68 39 7 5

TABLE III HEC Additives at 0.25% (bwoc) CEMENT HEIGHT (mL)/INTERMEDIATEHEIGHT (mL) Exhibits # Additive 0 min 5 min 10 min 20 min 30 min 60 minCohesion 1 HEC 250 HHR  52/0  52/0 54/0 56/0 56/0 57/0 YES 2 HEC 250GXRCP  58/0  64/0 63/0 62/0 62/0 60/70 NO 3 HEC 250 JR 204/234  78/23070/230 67/230 66/230 64/68 NO 4 HEC 250 LR 210/230 126/232 83/230 72/23068/230 65/230 NO

TABLE IV HEC Additives at 0.25% (bwoc) Rheology 600 # Additive rpm 300rpm 200 rpm 100 rpm 6 rpm 3 rpm 1 HEC 250 HHR >300 >300 >300 231 52 39 2HEC 250 GXRCP >300 194 157 117 71 63 3 HEC 250 JR 159 105 85 61 33 28 4HEC 250 LR 149 95 75 52 25 21

Based on the results set forth in Tables I-IV, the higher molecularweight HEC additives, namely HEC 250 HHR which has a molecular weight of1,300,000 g/mol was found to be an effective cement cohesion additive atconcentrations of 0.25% bwoc and 0.50% bwoc while HEC 250 GXRCP whichhas a molecular weight of 300,000 g/mol was found to be an effectivecement cohesion additive at a concentration of 0.50% bwoc. The lowermolecular weight HEC additive, namely HEC 250 LR PA which has amolecular weight of 90,000 g/mol. and blend of two HEC additives thatdid not have a specific molecular weight, namely HEC 250 LR were foundnot to be effective cement cohesion additives at the concentrationstested, i.e. 0.25% and 0.50% bwoc.

Further tests were conducted with HEC 250 HHR and HEC 250 GXRCP atvarious concentrations as set forth in Tables V-VIII as follows: TABLE VHEC 250 HHR CEMENT HEIGHT (mL)/INTERMEDIATE HEIGHT (mL) # % (bwoc) 0 min5 min 10 min 20 min 30 min 60 min Exhibits Cohesion 1 0.50% 53/0 52/052/0 52/0 52/0 52/0 YES 5 0.25% 52/0 52/0 54/0 56/0 56/0 57/0 YES 90.20% 52/224 54/223 55/224 57/223 57/222 58/220 YES 10 0.15% 56/22060/218 60/218 62/222 65/220 58/70 NO 11 0.10% 60/232 66/232 65/23166/230 66/228 68/226 NO 12 0.05% 64/238 67/230 62/230 62/230 61/23060/63 NO

TABLE VI HEC 250 HHR Rheology # % (bwoc) 600 rpm 300 rpm 200 rpm 100 rpm6 rpm 3 rpm 1 0.50% >300 >300 >300 >300 204 151 5 0.25% >300 >300 >300231 52 39 9 0.20% >300 >300 248 163 44 35 10 0.15% >300 210 159 103 4541 11 0.10% 246 144 112 74 49 42 12 0.05% 161 107 91 69 34 25

TABLE VII HEC 250 GXRCP CEMENT HEIGHT (mL)/INTERMEDIATE HEIGHT (mL) # %(bwoc) 0 min 5 min 10 min 20 min 30 min 60 min Exhibits Cohesion 2 0.50%53/212 61/220 60/218 60/218 50/60 50/68 YES 13 0.45% 62/240 70/24067/240 66/238 65/238 64/230 YES 14 0.35% 58/228 66/230 64/225 64/22464/224 62/74 NO 6 0.25% 58/0 64/0 63/0 62/0 62/0 60/70 NO 15 0.15%60/230 78/230 73/228 70/220 69/220 67/0 NO

TABLE VIII HEC 250 GXRCP Rheology # % (bwoc) 600 rpm 300 rpm 200 rpm 100rpm 6 rpm 3 rpm 2 0.50% >300 >300 243 150 43 38 13 0.45% >300 270 203126 42 39 14 0.35% >300 265 205 138 69 62 6 0.25% >300 194 157 117 71 6315 0.15% 182 123 100 74 43 36

Based on the results set forth in Tables V-VIII, the HEC additive havinga molecular weight of 1,300,000 g/mol, namely HEC 250 HHR, was found tobe an effective cement cohesion additive at concentrations of at least0.20% bwoc while the HEC additive which having a molecular weight of300,000 g/mol, namely HEC 250 GXRCP, was found to be an effective cementcohesion additive at concentrations of at least 0.45% bwoc.

Further tests were conducted with mixtures of HEC 250 HHR and HEC 250GXRCP at ratios of 2:1, 1:1 and 1:2 at a concentration of 0.30% bwoc.The three blends were tested as dry-blended additives and as additivesthat were prehydrated in cement mix water. For the “prehydration” tests,step 2 in the above procedure was modified such that the water and HECadditive were mixed for 1 minute at 2000 rpm in the Waring blender tohydrate the additive, then the cement was added and mixing was continuedfor 2 minutes at 200 rpm. The results of these tests are set forth inTables IX-XIV as follows, wherein Tables XIII and XIV show the ratio ofHEC 250 GXRCP and HEC 250 HHR at a 2:1 ratio but at varyingconcentrations of 0.3%, 0.25%, 0.2%, 0.15% and 0.1% bwoc. TABLE IX HEC250 GXRCP and HEC 250 HHR Combined CEMENT HEIGHT (mL)/INTERMEDIATEHEIGHT (mL) Exhibits # % (bwoc) 0 min 5 min 10 min 20 min 30 min 60 minCohesion 16  0.1% GXRCP + 0.2% HHR 53/230 55/228 55/228 56/228 58/22659/226 YES 17  0.2% GXRCP + 0.1% HHR 52/230 65/230 64/230 64/230 64/23062/230 NO 18 0.15% GXRCP + 0.15% HHR 56/230 60/230 61/230 62/228 60/22858/228 NO

TABLE X HEC 250 GXRCP and HEC 250 HHR Combined Rheology # % (bwoc) 600rpm 300 rpm 200 rpm 100 rpm 6 rpm 3 rpm 16 0.1% GXRCP + 0.2%HHR >300 >300 >300 209 48 41 17 0.2% GXRCP + 0.1% HHR >300 >300 278 17669 65 18 0.15% GXRCP + 0.15% HHR >300 >300 >300 221 77 72

TABLE XI HEC 250 GXRCP and HEC 250 HHR Combined (PREHYDRATED) CEMENTHEIGHT (mL)/ INTERMEDIATE HEIGHT (mL) Exhibits # % (bwoc) 0 min 5 min 10min 20 min 30 min 60 min Cohesion 16  0.1% GXRCP + 0.2% HHR 56/22857/228 57/228 57/228 58/228 58/220 YES 17  0.2% GXRCP + 0.1% HHR 55/23460/232 59/230 59/230 59/230 58/230 YES 18 0.15% GXRCP + 0.15% HHR 55/23357/230 57/230 57/230 56/230 56/230 NO

TABLE XII EC 250 GXRCP and HEC 250 HHR Combined (PREHYDRATED) Rheology #% (bwoc) 600 rpm 300 rpm 200 rpm 100 rpm 6 rpm 3 rpm 16  0.1% GXRCP +0.2% HHR >300 >300 >300 239 77 70 17  0.2% GXRCP + 0.1% HHR >300 >300267 173 72 69 18 0.15% GXRCP + 0.15% HHR >300 >300 >300 208 81 75

TABLE XIII HEC 250 GXRCP and HEC 250 HHR Combined (PREHYDRATED) 2:1RATIO CEMENT HEIGHT (mL)/ INTERMEDIATE HEIGHT (mL) Exhibits # % (bwoc) 0min 5 min 10 min 20 min 30 min 60 min Cohesion 17  0.2% GXRCP + 0.1% HHR55/234 60/232 59/230 59/230 59/230 58/230 YES 21 0.167% GXRCP + 0.083%HHR 58/232 63/230 62/230 62/230 62/230 60/230 NO 22 0.133% GXRCP +0.067% HHR 55/242 74/234 72/230 71/230 70/230 69/230 NO 23  0.10%GXRCP + 0.05% HHR 55/238 66/235 66/232 66/230 64/230 64/230 NO 24 0.067%GXRCP + 0.033% HHR 52/238 64/234 62/230 62/230 61/230 60/230 NO

TABLE XIV HEC 250 GXRCP and HEC 250 HHR Combined (PREHYDRATED) 2:1 RATIORheology # % (bwoc) 600 rpm 300 rpm 200 rpm 100 rpm 6 rpm 3 rpm 17  0.2%GXRCP + 0.1% HHR >300 >300 267 173 72 69 21 0.167% GXRCP + 0.083%HHR >300 >300 237 156 73 71 22 0.133% GXRCP + 0.067% HHR >300 211 162104 50 49 23  0.10% GXRCP + 0.05% HHR >300 212 162 112 64 58 24 0.067%GXRCP + 0.033% HHR 226 135 109 77 41 31

The results of Tables IX-XIV indicate that by combining differentmolecular weight HEC samples, the cement cohesion properties of the HECsamples can be increased while reducing the concentration of theindividual HEC samples. For instance, HEC 250 GXRCP alone was effectiveas a cement cohesion additive at a concentration of 0.45% while HEC 250HHR alone was effective as a cement cohesion additive at a concentrationof 0.2% (See Tables V and VII). By combining HEC 250 GXRCP and HEC 250HHR (see blend number 17 in Tables IX-XIV which included 0.2% HEC 250GXRCP and 0.1% HEC 250 HHR), the concentrations of the HEC samples werereduced to 0.2% and 0.1%, respectively, without compromising theeffectiveness of the blend as a cement cohesion additive.

As shown in Tables XI-XIV, prehydration of the HEC can increase theeffectiveness of the cohesion properties of the cement cohesionadditive. For instance, blend number 17 did not exhibit cohesion whendry blended (Table IX) but did exhibit good cohesion properties when thecement cohesion additive was prehydrated (Table XI and XIII).

Although only a few exemplars of this embodiment have been described indetail above those skilled in the art will readily appreciate that manyother modifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of thisembodiment. Accordingly, all such modifications are intended to beincluded within the scope of this embodiment as defined in the followingclaims.

1. A cementing composition for sealing a subterranean zone comprising:cement; an effective amount of a polymeric cement cohesion additivesufficient to inhibit one or both of contamination and dilution of thecementing composition by fluids in the subterranean zone; and water. 2.The composition of claim 1 wherein the polymeric cement cohesionadditive comprises hydroxyethylcellulose.
 3. The composition of claim 2wherein the hydroxyethylcellulose has a molecular weight of at least300,000 g/mol.
 4. The composition of claim 2 wherein thehydroxyethylcellulose has a molecular weight of at least 1,300,000g/mol.
 5. The composition of claim 2 wherein the hydroxyethylcellulosecomprises a mixture of hydroxyethylcellulose having a molecular weightof at least 1,300,000 g/mol. and hydroxyethylcellulose having amolecular weight of at least 300,000 g/mol.
 6. The composition of claim3 wherein the composition comprises at least about 0.45 percent ofhydroxyethylcellulose by weight of the cement.
 7. The composition ofclaim 4 wherein the composition comprises at least about 0.2 percent ofhydroxyethylcellulose by weight of the cement.
 8. The composition ofclaim 5 wherein the composition comprises at least about 0.3 percent ofhydroxyethylcellulose by weight of the cement.
 9. The composition ofclaim 1 wherein the cement is Portland cement, pozzolan cement, gypsumcement, aluminous cement, silica cement, or alkaline cement.
 10. Thecomposition of claim 9 wherein the cement is class A, G or H Portlandcement.
 11. The composition of claim 1 wherein the water is present in arange of 35-65 percent by weight of the cement.
 12. The composition ofclaim 1 further comprising a mixture of foaming and foam stabilizingsurfactants present in an amount sufficient to form and stabilize afoamed cementing composition.
 13. The composition of claim 12 whereinthe mixture of foaming and foam stabilizing surfactants is comprised ofan ethoxylated alcohol ether sulfate present in an amount of about 63.3parts by weight, cocoylamidopropylbetaine present in an amount of about31.7 parts by weight and cocoylamidopropyldimethylamine oxide present inan amount of about 5 parts by weight.
 14. The composition of claim 13wherein the mixture of foaming and foam stabilizing surfactants in a 30%to 50% aqueous solution is present in an amount in the range of fromabout 1% to about 3% by volume of water therein.
 15. The composition ofclaim 12 wherein the cementing composition further comprises sufficientgas to form a foam.
 16. The composition of claim 15 wherein the gas isselected from the group consisting of air and nitrogen.
 17. Thecomposition of claim 16 wherein the gas is present in the composition inan amount in the range of from about 15% to about 30% by volume of thecomposition.
 18. The composition of claim 1 further comprising one ormore of a slurry density modifying material, dispersing agent, setretarding agent, set accelerating agent, fluid loss control agent,strength retrogression control agent, viscosifying agent, foaming agent,and foam stabilizing agent.
 19. A cementing composition for sealing asubterranean zone comprising: at least one hydraulic cement selectedfrom the group consisting of Portland cement, pozzolan cement, gypsumcement, aluminous cement, silica cement and alkaline cement; aneffective amount of a polymeric cement cohesion additive comprisinghydroxyethylcellulose sufficient to inhibit one or both of contaminationand dilution of the cementing composition by fluids in the subterraneanzone; water in an amount of from 35 to 65 percent by weight of thecement; and one or more additive selected from the group consisting of aslurry density modifying material, a dispersing agent, a set retardingagent, a set accelerating agent, a fluid loss control agent, a strengthretrogression control agent, a viscosifying agent, a foaming agent, anda foam stabilizing agent.
 20. A cementing composition for sealing asubterranean zone comprising: at least one hydraulic cement selectedfrom the group consisting of Portland cement, pozzolan cement, gypsumcement, aluminous cement, silica cement and alkaline cement; aneffective amount of a polymeric cement cohesion additive comprisinghydroxyethylcellulose sufficient to inhibit one or both of contaminationand dilution of the cementing composition by fluids in the subterraneanzone; water in an amount of from 35 to 65 percent by weight of thecement; and a mixture of foaming and foam stabilizing surfactantspresent in an amount sufficient to form and stabilize a foamed cementingcomposition.